Electronic apparatus

ABSTRACT

The electronic apparatus comprises a display portion and a quartz crystal oscillator at least, and said electronic apparatus comprises at least one quartz crystal oscillator. Also, the at least one oscillator comprises a quartz crystal oscillating circuit comprising an amplification circuit and a feedback circuit. The feedback circuit is constructed by a flexural mode, quartz crystal tuning fork resonator or a length-extensional mode quartz crystal resonator and for example, the quartz crystal tuning fork resonator comprising tuning fork tines and tuning fork base that are formed integrally, is shown with novel shape and electrode construction. Also, the quartz crystal tuning fork resonator, capable of vibrating in a fundamental mode and having a high frequency stability can be provided with a small series resistance and a high quality factor, even when the tuning fork resonator is miniaturized. In addition, from a relationship of an amplification rate and a feedback rate, an output signal of the quartz crystal oscillating circuit having a frequency of the fundamental mode vibration for the quartz crystal tuning fork resonator can be provided with the high frequency stability.

FIELD OF THE INVENTION

[0001] The present invention relates to an electronic apparatus comprising a display portion and a quartz crystal oscillator at least.

BACKGROUND OF THE INVENTION

[0002] There are many electronic apparatus comprising a display portion and a quartz crystal oscillator at least. For example, cellular phones, wristwatches, facsimiles and pagers comprising a quartz crystal oscillator are well known. Recently, because of high stability for frequency, miniaturization and the light weight nature of these electronic apparatus, the need for an electronic apparatus comprising a smaller quartz crystal oscillator with a high frequency stability has arisen. For example, the quartz crystal oscillator with a quartz crystal tuning fork resonator, which is capable of vibrating in a flexural mode, is widely used as a time standard in an electronic apparatus such as the cellular phones, the wristwatches, the facsimiles and the pagers. Similar to this, the same need has also arisen for an electronic apparatus comprising a length-extensional mode quartz crystal resonator with a frequency of 1 MHz to 6 MHz to decrease an electric current consumption of the electronic apparatus.

[0003] Heretofore, however, it has been impossible to obtain an electronic apparatus comprising a smaller quartz crystal oscillator with a conventional miniaturized quartz crystal tuning fork resonator, capable of vibrating in a flexural mode, and having a high frequency stability, a small series resistance and a high quality factor. When miniaturized, the conventional quartz crystal tuning fork resonator capable of vibrating in a flexural mode, as shown in FIG.12 (which has electrodes on the obverse faces 203, 207, reverse faces 204, 208 and the four sides 205, 206, 209, 210 of each tuning fork tine, as also shown in FIG.13—a cross-sectional view of tuning fork tines of FIG.12), it has a smaller electromechanical transformation efficiency because the resonator shape and the electrode construction provide a small electric field (i.e. Ex becomes small), as a result of which the resonator has a low frequency stability, a large series resistance and a reduced quality factor. In FIG.12, a conventional tuning fork resonator 200 is shown with tines 201, 202 and a base 230.

[0004] Moreover, for example, Japanese Patent Nos. P56-65517 and P2000-223992A and International Patent No. WO 00/44092 were published and teach grooves and electrodes constructed at tuning fork tines of a flexural mode, tuning fork, quartz crystal resonator. However, they teach nothing about a quartz crystal oscillator of the present invention having novel shape, novel electrode construction and figure of merit M for a quartz crystal tuning fork resonator, capable of vibrating in a flexural mode and about a relationship of an amplification circuit and a feedback circuit which construct a quartz crystal oscillating circuit.

[0005] Additionally, for example, there has been a big problem in the conventional oscillator with the conventional quartz crystal tuning fork resonator, such that a fundamental mode vibration of the resonator jumps to a second overtone mode vibration by shock or vibration.

[0006] Similarly, however, it has been impossible to obtain an electronic apparatus comprising a smaller quartz crystal oscillator with a conventional length-extensional mode quartz crystal resonator, capable of vibrating in a length-extensional mode, and having a frequency of 1 MHz to 6 MHz, a small series resistance and a high quality factor. As an example of a length-extensional mode quartz crystal resonator of the prior art, the length-extensional mode resonator comprising a vibrational portion, connecting portions and supporting portions, which is formed from a Z plate perpendicular to z axis, is well known, and this resonator is formed integrally by a chemical etching process. Also, electrodes are disposed opposite each other on sides of the vibrational portion formed by the chemical etching process so that the electrodes disposed opposite each other are of opposite electrical polarity.

[0007] Also, a cutting angle of the conventional length-extensional mode quartz crystal resonator is generally within a range of ZYw(0° -+5°), according to an IEEE notation. In detail, the connecting portions are connected opposite each other at both end portions of a width of the vibrational portion and at a central portion of the length direction thereof. Namely, the direction of the connecting portions constructed opposite each other corresponds to the direction of the electric field.

[0008] Now, when an alternating current(AC) voltage is applied between the electrodes, an electric field occurs alternately in the width direction, as a result, the resonator is capable of vibrating in the length direction, but the electric field of between the electrodes becomes very small because quartz crystal is an anisotropic material and the sides of the vibrational portion have a complicated shape formed by the chemical etching process. Namely, the resonator has a smaller electromechanical transformation efficiency because the resonator shape and the electrode construction provide a small electric field, consequently, the resonator has a low frequency stability, a large series resistance and a reduced quality factor when it has the frequency of 1 MHz to 6 MHz.

[0009] It is, therefore, a general object of the present invention to provide embodiments of an electronic apparatus and a quartz crystal oscillator, which constructs an electronic apparatus of the present invention, comprising a quartz crystal oscillating circuit with a flexural mode, quartz crystal tuning fork resonator, capable of vibrating in a fundamental mode, and having a high frequency stability, a small series resistance and a high quality factor, or embodiments of a quartz crystal oscillator, which also constructs an electronic apparatus of the present invention, comprising a quartz crystal oscillating circuit with a length-extensional mode quartz crystal resonator having a frequency of 1 MHz to 6 MHz, a small series resistance and a high quality factor, which overcome or at least mitigate one or more of the above problems.

SUMMARY OF THE INVENTION

[0010] The present invention relates to an electronic apparatus comprising a display portion and a quartz crystal oscillator at least, and the quartz crystal oscillator comprises a quartz crystal oscillating circuit having an amplification circuit and a feedback circuit, and in particular, relates to a quartz crystal oscillator having a flexural mode, quartz crystal tuning fork resonator capable of vibrating in a fundamental mode and having an output signal of a high frequency stability for the fundamental mode vibration of the resonator, and also to a quartz crystal oscillator having a suppressed second overtone mode vibration of the flexural mode, quartz crystal tuning fork resonator, in addition, relates to a quartz crystal oscillator comprising a length-extensional mode quartz crystal resonator. The quartz crystal oscillators are, therefore, available for the electronic apparatus requiring miniaturized and low priced quartz crystal oscillators with high time accuracy and shock proof.

[0011] It is an object of the present invention to provide an electronic apparatus comprising a quartz crystal oscillator with a miniature quartz crystal tuning fork resonator, capable of vibrating in a flexural mode, and having a high frequency stability, a small series resistance R₁ and a high quality factor Q₁, whose frequency for a fundamental mode vibration is within a range of 10 kHz to 200 kHz.

[0012] It is an another object of the present invention to provide an electronic apparatus comprising a quartz crystal oscillator with a flexural mode, quartz crystal tuning fork resonator, capable of vibrating in a fundamental mode, and having a high frequency stability which gives a high time accuracy.

[0013] It is a further object of the present invention to provide an electronic apparatus comprising a quartz crystal oscillator with a length-extensional mode quartz crystal resonator.

[0014] According to one aspect of the present invention, there is provided an electronic apparatus comprising a display portion and a quartz crystal oscillator at least, and said electronic apparatus having one quartz crystal oscillator, said one quartz crystal oscillator comprising: a quartz crystal oscillating circuit comprising; an amplification circuit comprising an amplifier at least and a feedback circuit comprising a quartz crystal resonator and capacitors at least, said quartz crystal resonator being a quartz crystal tuning fork resonator capable of vibrating in a flexural mode, and said quartz crystal tuning fork resonator comprising: tuning fork tines each of which has a length, a width and a thickness and the length greater than the width and the thickness; and a tuning fork base; said tuning fork tines and said tuning fork base that are formed integrally; and electrodes disposed facing each other on sides of said tuning fork tines so that the electrodes disposed facing each other are of opposite electrical polarity and said tuning fork tines are capable of vibrating in inverse phase.

[0015] According to a second aspect of the present invention there is provided an electronic apparatus comprising a display portion and a quartz crystal oscillator at least, and said electronic apparatus comprises at least one quartz crystal oscillator comprising: an oscillating circuit comprising; an amplification circuit comprising an amplifier at least, and a feedback circuit comprising a length-extensional mode quartz crystal resonator.

[0016] According to a third aspect of the present invention, there is provided a method for manufacturing an electronic apparatus comprising a display portion and a quartz crystal oscillator at least, and said electronic apparatus comprising at least one quartz crystal oscillator, said at least one oscillator comprising: a quartz crystal oscillating circuit comprising; an amplification circuit comprising an amplifier at least, and a feedback circuit comprising a quartz crystal resonator and capacitors at least, said quartz crystal resonator being a quartz crystal tuning fork resonator capable of vibrating in a flexural mode, said quartz crystal tuning fork resonator comprising the steps of: forming integrally tuning fork tines each of which has a length, a width and a thickness and the length greater than the width and the thickness and a tuning fork base; disposing electrodes facing each other on sides of said tuning fork tines so that the electrodes disposed facing each other are of opposite electrical polarity and said tuning fork tines are capable of vibrating in inverse phase; and adjusting resonance frequency of said quartz crystal tuning fork resonator after mounting it at a mounting portion by conductive adhesives or solder so that a frequency deviation is within a range of −100 PPM to +100 PPM.

[0017] Preferably, said tuning fork resonator is constructed so that figure of merit M₁ of a fundamental mode vibration is larger than figure of merit M₂ of a second overtone mode vibration.

[0018] Preferably, the quartz crystal oscillator with said tuning fork resonator is constructed so that a ratio of an amplification rate α₁ of the fundamental mode vibration and an amplification rate α₂ of the second overtone mode vibration of said amplification circuit is larger than that of a feedback rate β₂ of the second overtone mode vibration and a feedback rate β₁ of the fundamental mode vibration of said feedback circuit, and a product of the amplification rate α₁ and the feedback rate β₁ of the fundamental mode vibration is larger than 1.

[0019] Preferably, the quartz crystal oscillator with said tuning fork resonator is constructed so that a ratio of an absolute value of negative resistance, |−RL₁|of the fundamental mode vibration of said amplification circuit and series resistance R₁ of the fundamental mode vibration is larger than that of an absolute value of negative resistance, |-RL₂|of the second overtone mode vibration of said amplification circuit and series resistance R₂ of the second overtone mode vibration.

[0020] Preferably, the length-extensional mode quartz crystal resonator comprises a vibrational portion, connecting portions and supporting portions, which are formed integrally by a particle method.

[0021] The present invention will be more fully understood by referring to the following detailed specification and claims taken in connection with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 shows a block diagram of an embodiment of an electronic apparatus of the present invention, and illustrating the diagram of a facsimile apparatus;

[0023]FIG. 2 shows a diagram of an embodiment of a quartz crystal oscillating circuit constructing a quartz crystal oscillator, which constructs an electronic apparatus of the present invention;

[0024]FIG. 3 shows a diagram of the feedback circuit of FIG. 2;

[0025]FIG. 4 shows a general view of a flexural mode, quartz crystal tuning fork resonator constructing a quartz crystal oscillator, which constructs an electronic apparatus of the first embodiment of the present invention;

[0026]FIG. 5 shows a D-D′ cross-sectional view of the tuning fork base of FIG. 4, and illustrating electrode construction;

[0027]FIG. 6 shows a plan view of a quartz crystal tuning fork resonator of FIG. 4;

[0028]FIG. 7 shows a plan view of a flexural mode, quartz crystal tuning fork resonator constructing a quartz crystal oscillator, which constructs an electronic apparatus of the second embodiment of the present invention;

[0029]FIG. 8a and FIG. 8b show a top view and a side view of a length-extensional mode quartz crystal resonator constructing a quartz crystal oscillator, which constructs an electronic apparatus of the third embodiment of the present invention;

[0030]FIG. 9 shows a cross-sectional view of a quartz crystal unit constructing a quartz crystal oscillator, which constructs an electronic apparatus of the fourth embodiment of the present invention;

[0031]FIG. 10 shows a cross-sectional view of a quartz crystal oscillator, which constructs an electronic apparatus of the fifth embodiment of the present invention;

[0032]FIG. 11 shows a step diagram of a method for manufacturing a quartz crystal unit constructing a quartz crystal oscillator, which constructs an electronic apparatus of the present invention;

[0033]FIG. 12 is a general view of the conventional flexural mode, quartz crystal tuning fork resonator constructing a quartz crystal oscillator of the prior art, which constructs the conventional electronic apparatus; and

[0034]FIG. 13 is a cross-sectional view of the tuning fork tines of FIG. 12, and illustrating electrode construction.

DETAILED DESCRIPTION

[0035] Referring now to the drawings, the embodiments of the present invention will be described in more detail.

[0036]FIG. 1 shows a block diagram of an embodiment of an electronic apparatus of the present invention, and illustrating the diagram of a facsimile apparatus. As is shown in FIG. 1, the apparatus generally comprises a modem, a phonetic circuit, a timepiece circuit, a printing portion, a taking portion, an operation portion and a display portion. In this principle, perception and scanning of reflection light of light projected on manuscript in the taking portion are performed by CCD(Charge Coupled Device), in addition, light and shade of the reflection light are transformed into a digital signal, and the signal is modulated by the modem and is sent to a phone line(Communication line). Also, in a receiving side, a received signal is demodulated by the modem and is printed on a paper in the print portion by synchronizing the received signal with a signal of a sending side.

[0037] As shown in FIG. 1, a quartz crystal resonator is used as a CPU clock of the control portion and the printing portion, and as a clock of the phonetic circuit and the modem, and as a time standard of the timepiece. Namely, the resonator constructs a quartz crystal oscillator and an output signal of the oscillator is used. For example, it is used as a signal to display time at the display portion. In order to get the facsimile apparatus of this embodiment which operates normally, an accuracy output signal of the oscillator is required for the facsimile apparatus, which is one of the electronic apparatus of the present invention. Also, a digital display and an analogue display are included in the display of the present invention.

[0038] In this embodiment, though the facsimile apparatus is shown as an example of an electronic apparatus, the present invention is not limited to this, namely, the present invention includes all electronic apparatus comprising a quartz crystal oscillator, for example, cellar phone, telephone, TV set, camera, video set, video camera, pagers, personal computer, printer, CD player, MD player, electronic musical instrument, car navigator, car electronics, timepiece, IC card and so forth.

[0039]FIG. 2 shows a diagram of an embodiment of a quartz crystal oscillating circuit constructing a quartz crystal oscillator, which constructs an electronic apparatus of the present invention. The quartz crystal oscillating circuit 1 comprises an amplifier (CMOS Inverter) 2, a feedback resistor 4, drain resistor 7, capacitors 5, 6 and a flexural mode, quartz crystal tuning fork resonator 3. Namely, the oscillating circuit 1 comprises an amplification circuit 8 having the amplifier 2 and the feedback resistor 4, and a feedback circuit 9 having the drain resistor 7, the capacitors 5, 6 and the quartz crystal tuning fork resonator 3. In addition, an output signal of the oscillating circuit 1 comprising the quartz crystal tuning fork resonator 3, capable of vibrating in a fundamental mode, is outputted through a buffer circuit (not shown in FIG. 2).

[0040] In detail, a frequency of the fundamental mode vibration is outputted through a buffer circuit as an output signal. According to the present invention, the frequency of the fundamental mode vibration of the resonator is within a range of 10 kHz to 200 kHz. Especially, 32.768 kHz is used widely. In more detail, the quartz crystal oscillator in this embodiment comprises the quartz crystal oscillating circuit and the buffer circuit, namely, the quartz crystal oscillating circuit comprises the amplification circuit and the feedback circuit, and the amplification circuit comprises the amplifier at least and the feedback circuit comprises the flexural mode, quartz crystal tuning fork resonator and the capacitors at least. Also, flexural mode, quartz crystal tuning fork resonators which are used in a quartz crystal oscillator will be described in FIG. 4-FIG. 7 in detail. Instead of the flexural mode, quartz crystal tuning fork resonator, a length-extensional mode quartz crystal resonator may be used.

[0041]FIG. 3 shows a diagram of the feedback circuit of FIG. 2. Now, when angular frequency ω_(i) of the flexural mode, quartz crystal tuning fork resonator 3, capable of vibrating in a flexural mode, a resistance R_(d) of the drain resistor 7, capacitance C_(g), C_(d) of the capacitors 5, 6, crystal impedance R_(ei) of the quartz crystal resonator 3, an input voltage V₁, and an output voltage V₂ are taken, a feedback rate β_(i) is defined by β_(i)=|V₂|_(i)/|V₁|_(i), where i shows vibration order, for example, when i=1 and 2, they are for a fundamental mode vibration and a second overtone mode vibration.

[0042] In addition, load capacitance C_(L) is given by C_(L)=C_(g) C_(d)/(C_(g)+C_(d)), and when C_(g)=C_(d)=C_(gd) and Rd>>R_(ei), the feedback rate β_(i) is given by β_(i)=1/(1+kC_(L) ²), where k is expressed by a function of ω_(i), R_(d) and R_(ei). Also, R_(ei) is approximately equal to series resistance R_(i).

[0043] Thus, it is easily understood from a relationship of the feedback rate β_(i) and load capacitance C_(L) that the feedback rate of resonance frequency for a fundamental mode vibration and an overtone mode vibration becomes large, respectively, according to decrease of load capacitance C_(L). Therefore, when C_(L) has a small value, an oscillation of the overtone mode occurs very easily, instead of that of the fundamental mode. This is the reason why a maximum amplitude of the overtone mode vibration becomes smaller than that of the fundamental mode vibration, and the oscillation of the overtone mode satisfies an amplitude condition and a phase condition simultaneously which are the continuous condition of an oscillation in an oscillating circuit.

[0044] As it is also one object of the present invention to provide a quartz crystal oscillator having a flexural mode, quartz crystal tuning fork resonator, capable of vibrating in a fundamental mode and having a high frequency stability (high time accuracy) of an output signal, and having reduced electric current consumption, in this embodiment, load capacitance C_(L) is less than 10 pF to reduce electric current consumption. To get much reduced electric current consumption, C_(L) is preferably less than 8 pF because electric current consumption is proportional to C_(L). Here, C_(L) does not include stray capacity of an oscillating circuit. Actually, there exists the stray capacity by constructing the oscillating circuit. Therefore, in this embodiment, load capacitance C_(L) including the stray capacity by constructing the circuit is less than 18 pF.

[0045] In addition, in order to suppress a second overtone mode vibration and to obtain a quartz crystal oscillator having an output signal of a frequency of a fundamental mode vibration, the quartz crystal oscillator in this embodiment is constructed so that it satisfies a relationship of α₁/α₂>β₂/β₁ and α₁β₁>1, where α₁ and α₂ are, respectively, an amplification rate of the fundamental mode vibration and the second overtone mode vibration of an amplification circuit, and β₁ and β₂ are, respectively, a feedback rate of the fundamental mode vibration and the second overtone mode vibration of a feedback circuit.

[0046] In other words, the quartz crystal oscillator is constructed so that a ratio of the amplification rate α₁ of the fundamental mode vibration and the amplification rate α₂ of the second overtone mode vibration of the amplification circuit is larger than that of the feedback rate β₂ of the second overtone mode vibration and the feedback rate β₁ of the fundamental mode vibration of the feedback circuit, and a product of the amplification rate α₁ and the feedback rate β₁ of the fundamental mode vibration is larger than 1. A description of the high frequency stability will be performed later.

[0047] Also, characteristics of the amplifier of the amplification circuit constructing the quartz crystal oscillating circuit of this embodiment can be expressed by negative resistance −RL_(i). For example, when i=1, negative resistance −RL₁ is for a fundamental mode vibration and when i=2, negative resistance −RL₂ is for a second overtone mode vibration. In this embodiment, the quartz crystal oscillating circuit is constructed so that a ratio of an absolute value of negative resistance, |−RL₁| of the fundamental mode vibration of the amplification circuit and series resistance R₁ of the fundamental mode vibration is larger than that of an absolute value of negative resistance, |−RL₂| of the second overtone mode vibration of the amplification circuit and series resistance R₂ of the second overtone mode vibration. That is to say, the oscillating circuit is constructed so that it satisfies a relationship of |−RL₁|/R₁>|−RL₂|/R₂. By constructing the oscillating circuit like this, an oscillation of the second overtone mode can be suppressed, as a result of which an output signal of a frequency of the fundamental mode vibration can be provided because an oscillation of the fundamental mode generates easily in the oscillating circuit.

[0048]FIG. 4 shows a general view of a flexural mode, quartz crystal tuning fork resonator 10 constructing a quartz crystal oscillator, which constructs an electronic apparatus of the first embodiment of the present invention and its coordinate system o-xyz. A cut angle θ, which has a typical value of 0° to 10°, is rotated from a Z-plate perpendicular to the z axis about the x axis. The resonator 10 comprises two tuning fork tines 20 and 26 and a tuning fork base 40. The tines 20 and 26 have grooves 21 and 27 respectively, with the grooves 21 and 27 extending into the base 40. In addition, the base 40 has the additional grooves 32 and 36.

[0049]FIG. 5 shows a D-D′ cross-sectional view of the tuning fork base 40 for the quartz crystal resonator 10 of FIG. 4. In FIG. 5, the shape of the electrode construction within the base 40 for the quartz crystal resonator of FIG. 4 is described in detail. The section of the base 40 which couples to the tine 20 has the grooves 21 and 22 cut into the obverse and reverse faces of the base 40. Also, the section of the base 40 which couples to the tine 26 has the grooves 27 and 28 cut into the obverse and reverse faces of the base 40. In addition to these grooves, the base 40 has the grooves 32 and 36 cut between the grooves 21 and 27, and also, the base 40 has the grooves 33 and 37 cut between the grooves 22 and 28.

[0050] Furthermore, the grooves 21 and 22 have the first electrodes 23 and 24 both of the same electrical polarity, the grooves 32 and 33 have the second electrodes 34 and 35 both of the same electrical polarity, the grooves 36 and 37 have the third electrodes 38 and 39 both of the same electrical polarity, the grooves 27 and 28 have the fourth electrodes 29 and 30 both of same electrical polarity and the sides of the base 40 have the fifth and sixth electrodes 25 and 31, each of opposite electrical polarity. In more detail, the fifth, fourth, and second electrodes 25, 29, 30, 34 and 35 have the same electrical polarity, while the first, sixth and third electrodes 23, 24, 31, 38 and 39 have the opposite electrical polarity to the others. Two electrode terminals E-E′ are constructed. That is, the electrodes disposed inside the grooves constructed opposite each other in the thickness (z axis) direction have the same electrical polarity. Also, the electrodes disposed opposite each other across adjoining grooves have opposite electrical polarity.

[0051] In addition, the resonator has a thickness t of the tines or the tines and the base, and a groove thickness t₁. It is needless to say that the electrodes are disposed inside the grooves and on the sides of the tines. In this embodiment, the first electrodes 23 and 24 are disposed at the tine and the base, and also, the fourth electrodes 29 and 30 are disposed at the tine and the base. In addition, the electrodes are disposed on the sides of the tines opposite each other to the electrodes disposed inside the grooves. Namely, the electrodes are disposed opposite each other inside the grooves and on the sides of the tines so that the electrodes disposed opposite each other are of opposite electrical polarity. Additionally, the electrodes are disposed facing each other on the sides of the tines so that the electrodes disposed facing each other are of opposite electrical polarity and the tines are capable of vibrating in inverse phase.

[0052] Now, when a direct voltage is applied between the electrode terminals E-E′ (E terminal: plus, E′ terminal: minus), an electric field E_(x) occurs in the arrow direction as shown in FIG. 5. As the electric field E_(x) occurs perpendicular to the electrodes disposed on the base, the electric field E_(x) has a very large value and a large distortion occurs at the base, so that the quartz crystal tuning fork resonator is obtained with a small series resistance R₁ and a high quality factor Q₁, even if it is miniaturized.

[0053]FIG. 6 shows a plan view of the resonator 10 of FIG. 4. In FIG. 6, the construction and the dimension of grooves 21, 27, 32 and 36 are described in detail. The groove 21 is constructed to include a portion of the central line 41 of the tine 20, the groove 27 is similarly constructed to include a portion of the central line 42 of the tine 26. The width W₂ of the grooves 21 and 27 (groove width W₂) which include a portion of the central lines 41 and 42 respectively, is preferable because moment of inertia of the tines 20 and 26 becomes large and the tines can vibrate in a flexural mode easily. As a result, the quartz crystal tuning fork resonator capable of vibrating in a fundamental mode can be obtained with a small series resistance R₁ and a high quality factor Q₁.

[0054] In more detail, when part widths W₁, W₃ and groove width W₂ are taken, the tine width W of the tines 20 and 26 has a relationship of W=W₁+W₂+W₃, and a part or all of at least one of the grooves is constructed so that W₁≧W₃ or W₁<W₃. In addition, the groove width W₂ is constructed so that W₂≧W₁, W₃. In this embodiment, also, the grooves are constructed at the tines so that a ratio(W₂/W) of the groove width W₂ and the tine width W is larger than 0.35 and less than 1, and a ratio(t₁/t) of the groove thickness t₁ and the thickness t of the tines (tine thickness t) is less than 0.79, to obtain very large moment of inertia of the tines. That is, the flexural mode, quartz crystal tuning fork resonator, capable of vibrating in the fundamental mode, and having a high frequency stability can be provided with a small series resistance R₁, a high quality factor Q₁ and a small capacitance ratio r₁ because electromechanical transformation efficiency of the resonator becomes large markedly.

[0055] Likewise, length l₁ of the grooves 21 and 27 of the tines 20 and 26 extends into the base 40 in this embodiment (which has a dimension of the length l₂ and the length l₃ of the grooves). Therefore, groove length and length of the tines are given by (l₁-l₃) and (l-l₂), respectively, and a ratio of (l₁-l₃) and (l-l₂) is within a range of 0.4 to 0.8 to get a flexural mode tuning fork resonator with series resistance R₁ of a fundamental mode vibration smaller than series resistance R₂ of a second overtone mode vibration.

[0056] Furthermore, the total length l is determined by the frequency requirement and the size of the housing case. Simultaneously, to get a flexural mode, quartz crystal tuning fork resonator capable of vibrating in a fundamental mode with suppression of the second overtone mode vibration which is unwanted mode vibration, there is a close relationship between the groove length l₁ and the total length l. Namely, a ratio(l₁/l) of the groove length l₁ and the total length I is within a range of 0.2 to 0.78 because the quantity of charges which generate within the grooves and on the sides of the tines or the tines and the base can be controlled by the ratio, as a result, the second overtone mode vibration, which is unwanted mode vibration, can be suppressed, and simultaneously, a frequency stability of the fundamental mode vibration gets high. Therefore, the flexural mode, quartz crystal tuning fork resonator, capable of vibrating easily in the fundamental mode and having the high frequency stability can be provided.

[0057] In more detail, series resistance R₁ of the fundamental mode vibration becomes smaller than series resistance R₂ of the second overtone mode vibration. Namely, R₁<R₂, preferably, R₁<0.86R₂, therefore, a quartz crystal oscillator comprising an amplifier (CMOS inverter), capacitors, resistors and a quartz crystal unit with the quartz crystal tuning fork resonator of this embodiment can be obtained, which is capable of vibrating in the fundamental mode easily. In addition, in this embodiment the grooves 21 and 27 of the tines 20 and 26 extend into the base 40 in series, but embodiment of the present invention includes a plurality of grooves divided into the length direction of the tines. In addition, the grooves may be constructed only at the tines(l₃=0).

[0058] In this embodiment, the groove length l₁ corresponds to electrode length disposed inside the grooves, though the electrode is not shown in FIG. 6, but, when the electrode length is less than the groove length, the length l₁ is of the electrode length. Namely, the ratio(l₁/1) in this case is expressed by a ratio of electrode length l₁ of the grooves and the total length l. In order to achieve the above-mentioned object, it may be satisfied with at least one groove with the ratio constructed at the obverse and reverse faces of each tine. As a result, the flexural mode, quartz crystal tuning fork resonator, capable of vibrating very easily in the fundamental mode and having the high frequency stability can be realized. Also, a fork portion of this embodiment has a rectangular shape, but this invention is not limited to this, for example, the fork portion may have a U shape.

[0059] In addition, a space of between the tines is given by W₄, and in this embodiment, the space W₄ and the groove width W₂ are constructed so that W₄≧W₂, and more, the space W₄ is within a range of 0.05 mm to 0.35 mm and the width W₂ is within a range of 0.03 mm to 0.12 mm because it is easy to form a tuning fork shape and grooves of the tuning fork tines separately by a photo-lithographic process and an etching process, consequently, a frequency stability for a fundamental mode vibration gets higher than that for a second overtone mode vibration. In this embodiment, a quartz wafer with the thickness t of 0.05 mm to 0.15 mm is used.

[0060] In more detail, to obtain a flexural mode, quartz crystal tuning fork resonator with a high frequency stability which gives high time accuracy, it is necessary to obtain the resonator whose resonance frequency is not influenced by shunt capacitance because quartz crystal is a piezoelectric material and the frequency stability is very dependent on the shunt capacitance. In order to decrease the influence on the resonance frequency by the shunt capacitance, figure of merit M_(i) plays an important role. Namely, the figure of merit M_(i) that expresses inductive characteristics, electromechanical transformation efficiency and a quality factor of a flexural mode, quartz crystal tuning fork resonator, is defined by a ratio (Q_(i)/r_(i)) of a quality factor Q_(i) and capacitance ratio r_(i), namely, M_(i) is given by M_(i)=Q_(i)/r_(i), where i shows vibration order of the resonator, and for example, when i=1 and 2, figures of merit M₁ and M₂ are for a fundamental mode vibration and a second overtone mode vibration, respectively.

[0061] Also, a frequency difference Δf of resonance frequency f_(s) of mechanical series independent on the shunt capacitance and resonance frequency f_(r) dependent on the shunt capacitance is inversely proportional to the figure of merit M_(i). The larger the value M_(i) becomes, the smaller the difference Δf becomes. Namely, the influence on the resonance frequency f_(r) by the shunt capacitance decreases because it is close to the resonance frequency f_(s). Accordingly, the larger the M_(i) becomes, the higher the frequency stability of the flexural mode, quartz crystal tuning fork resonator becomes because the resonance frequency f_(r) of the resonator is almost never dependent on the shunt capacitance. Namely, the quartz crystal tuning fork resonator can be provided with a high time accuracy.

[0062] In detail, the quartz crystal tuning fork resonator capable of vibrating in a flexural mode can be obtained with figure of merit M₁ of a fundamental mode vibration larger than figure of merit M₂ of a second overtone mode vibration by the above-described tuning fork shape, grooves and dimensions. That is to say, M₁>M₂. As an example, when resonance frequency of a flexural mode, quartz crystal tuning fork resonator is about 32.768 kHz for a fundamental mode vibration and the resonator has a value of W₂/W=0.5, t₁/t=0.34 and l₁/l=0.48, though there is a distribution in production, the resonator has a value of M₁>65 and M₂ <30, respectively.

[0063] Namely, the flexural mode, quartz crystal tuning fork resonator which is capable of vibrating in the fundamental mode can be provided with high inductive characteristics, good electromechanical transformation efficiency (small capacitance ratio r₁ and small series resistance R₁) and a high quality factor. As a result, a frequency stability of the fundamental mode vibration becomes higher than that of the second overtone mode vibration, and simultaneously, the second overtone mode vibration can be suppressed because capacitance ratio r₂ and series resistance R₂ of the second overtone mode vibration become larger than capacitance ratio r₁ and series resistance R₁ of the fundamental mode vibration, respectively.

[0064] Therefore, the resonator capable of vibrating in the fundamental mode vibration can be provided with a high time accuracy because it has the high frequency stability. Consequently, a quartz crystal oscillator comprising the flexural mode, quartz crystal tuning fork resonator of this embodiment outputs a frequency of the fundamental mode vibration as an output signal, and the frequency of the output signal has a very high stability, namely, an excellent time accuracy. In other words, the quartz crystal oscillator of this embodiment has a remarkable effect such that a frequency change by ageing becomes extremely small. Also, resonance frequency of the resonator of this embodiment is adjusted so that a frequency deviation is within a range of −100 PPM to +100 PPM after mounting it at a mounting portion of a case or a lid by conductive adhesives or solder.

[0065] In addition, the groove thickness t₁ of the present invention is the thinnest thickness of the grooves because quartz crystal is an anisotropic material and the groove thickness t₁ has a distribution when it is formed by a chemical etching method. In the above-described embodiments, though the grooves are constructed at the tines, this invention is not limited to this, namely, a relationship of the figures of merit M₁ and M₂ can be applied to the conventional flexural mode, quartz crystal tuning fork resonator and a relationship of a quartz crystal oscillating circuit comprising an amplification circuit and a feedback circuit can be also applied to the conventional flexural mode, quartz crystal tuning fork resonator to suppress a second overtone mode vibration and to get a high frequency stability for a fundamental mode vibration.

[0066]FIG. 7 shows a plan view of a flexural mode, quartz crystal tuning fork resonator 45 constructing a quartz crystal oscillator, which constructs an electronic apparatus of the second embodiment of the present invention. The resonator 45 comprises tuning fork tines 46, 47 and a tuning fork base 48. The tines 46, 47 and the base 48 are formed integrally by a chemical etching process. In this embodiment, the base 48 has cut portions 53 and 54. Also, a groove 49 is constructed to include a portion of the central line 51 of the tine 46, a groove 50 is similarly constructed to include a portion of the central line 52 of the tine 47. In this embodiment, the grooves 49 and 50 are constructed at a part of the tines 46 and 47, and have groove width W₂ and groove length l₁. In more detail, groove area S (=W₂×l₁) has a value of 0.025 mm² to 0.12 mm² because it is very easy to form the grooves by a chemical etching process and the quartz crystal tuning fork resonator can be provided with good electromechanical transformation efficiency by the formation of the grooves.

[0067] Namely, the quartz crystal tuning fork resonator, capable of vibrating in a fundamental mode and having a high frequency stability can be provided with a small series resistance R₁ and a high quality factor Q₁. Therefore, a quartz crystal oscillator having the high frequency stability can be realized with an output signal of a frequency of the fundamental mode vibration. In this embodiment, though electrodes are not shown in FIG. 7, the electrodes are disposed inside the grooves 49, 50 and on sides of the tines 46 and 47, similar to the resonator of FIG. 4. In detail, the electrodes are disposed opposite each other inside the grooves and on the sides of the tines so that the electrodes disposed opposite each other are of opposite electrical polarity. Additionally, the electrodes are also disposed facing each other on the sides of the tines so that the electrodes disposed facing each other are of opposite electrical polarity.

[0068] In addition, the base 48 has cut portions 53 and 54, and the cut base 48 has a dimension of width W₅ (tines side) and width W₆ (opposite side to the tines side). When the base 48 is mounted at a mounting portion(e.g. on two lead wires for a package of tubular type) of a case or a lid of surface mounting type or tubular type by solder or conductive adhesives, it is necessary to satisfy W₆≧W₅ to decrease energy losses by vibration. The cut portions 53 and 54 are very effective to decrease the energy losses. Therefore, the flexural mode, quartz crystal tuning fork resonator, capable of vibrating in the fundamental mode and having the high frequency stability (high time accuracy) can be provided with a small series resistance R₁ and a high quality factor Q₁. Also, the width dimensions W=W₁+W₂+W₃ and W₄, and the length dimensions l₁, l₂ and l are as already described in relation to FIG. 6.

[0069]FIG. 8a and FIG. 8b are a top view and a side view for a length-extensional mode quartz crystal resonator constructing a quartz crystal oscillator, which constructs an electronic apparatus of the third embodiment of the present invention. The resonator 62 comprises vibrational portion 63, connecting portions 66, 69 and supporting portions 67, 80 including respective mounting portions 68, 81. In addition, the supporting portions 67 and 80 have respective holes 67 a and 80 a. Also, electrodes 64 and 65 are disposed opposite each other on upper and lower faces of the vibrational portion 63, the electrodes have opposite electrical polarities. Namely, a pair of electrodes is disposed on the vibrational portion. In this case, a fundamental mode vibration can be excited easily.

[0070] In addition, the electrode 64 extends to the mounting portion 81 through the one connecting portion 69 and the electrode 65 extends to the mounting portion 68 through the other connecting portion 66. In this embodiment, the electrodes 64 and 65 disposed on the vibrational portion 63 extend to the mounting portions of the different direction each other. But, the electrodes may be constructed in the same direction. The resonator in this embodiment is mounted on fixing portions of a case or a lid at the mounting portions 68 and 81 by conductive adhesives or solder.

[0071] Here, a cutting angle of the length-extensional mode quartz crystal resonator is shown. First, a quartz crystal plate perpendicular to x axis, so called, X plate quartz crystal is taken. Length L₀, width W₀ and thickness T₀ which are each dimension of the X plate quartz crystal correspond to the respective directions of y, z and x axes.

[0072] Next, this X plate quartz crystal is, first, rotated with an angle θ_(x) of −30° to +30° about the x axis, and second, rotated with an angle θ_(y) of −40° to +40° about y′ axis which is the new axis of the y axis. In this case, the new axis of the x axis changes to x′ axis and the new axis of the z axis changes to z″ axis because the z axis is rotated twice about two axes. The length-extensional mode quartz crystal resonator of the present invention is formed from the quartz crystal plate with the rotation angles.

[0073] In other words, according to an expression of IEEE notation, a cutting angle of the resonator of the present invention can be expressed by XYtl(−30°-+30°)/(−40°-+40°). By choosing a cutting angle of the resonator, a turn over temperature point T_(p) can be taken at an arbitrary temperature. In this embodiment, length L₀, width W₀ and thickness T₀ correspond to y′, z″ and x′ axes, respectively. But, when the X plate is rotated once about the x axis, the z″ axis corresponds to the z′ axis. In addition, the vibrational portion 63 has a dimension of length L₀ greater than width W₀ and thickness T₀ smaller than the width W₀. Namely, a coupling between length-extensional mode and width-extensional mode gets so small as it can be ignored, as a result of which, the quartz crystal resonator can vibrate in a single length-extensional mode.

[0074] In more detail, resonance frequency of the length-extensional mode resonator is inversely proportional to length L₀, and it is almost independent on such an other dimension as width W₀, thickness T₀, connecting portions and; supporting potions. Also, in order to obtain a length-extensional mode quartz crystal resonator with a frequency of 1 MHz to 6 MHz, the length L₀ is within a range of about 0.45 mm to about 2.7 mm. Thus, the miniature length-extensional mode resonator can be provided with the frequency.

[0075] Next, a value of a piezoelectric constant e₁₂ is described, which is of great importance and necessary to excite a length-extensional mode quartz crystal resonator of the present invention. The larger a value of this piezoelectric constant e₁₂ becomes, the higher an electromechanical transformation efficiency becomes. For example, the piezoelectric constant of the present invention e₁₂ is within a range of 0.095 C/m² to 0.18 C/m² approximately in an absolute value. Also, the piezoelectric constant e₁₂ in this embodiment can be calculated from the piezoelectric constants e₁₁=0.171 C/m² and e₁₄=−0.0406 C/m² of quartz crystal. It is easily understood that this is enough large to obtain a length-extensional mode quartz crystal resonator with a small series resistance R₁ and a high quality factor Q.

[0076] Now, when an alternating current voltage is applied between the electrodes 64 and 65 shown in FIG. 8b, an electric field E_(x) occurs alternately in the thickness direction, as shown by the arrow direction of the solid and broken lines in FIG. 8b. Consequently, the vibrational portion 63 is capable of extending and contracting in the length direction.

[0077]FIG. 9 shows a cross-sectional view of a quartz crystal unit constructing a quartz crystal oscillator, which constructs an electronic apparatus of the fourth embodiment of the present invention. The quartz crystal unit 170 comprises a flexural mode, quartz crystal tuning fork resonator 70, a case 71 and a lid 72. In more detail, the resonator 70 is mounted at a mounting portion 74 of the case 71 by conductive adhesives 76 or solder. Also, the case 71 and the lid 72 are connected through a connecting member 73. The resonator 70 in this embodiment is the same resonator as one of the flexural mode, quartz crystal tuning fork resonators 10 and 45 described in detail in FIG. 4-FIG. 7. Also, in this embodiment, circuit elements are connected at outside of the quartz crystal unit to get a quartz crystal oscillator. Namely, only the quartz crystal tuning fork resonator is housed in the unit and also, it is housed in the unit in vacuum. In this embodiment, the quartz crystal unit of surface mounting type is shown, but the quartz crystal tuning fork resonator may be housed in tubular type, namely the quartz crystal unit of tubular type. Also, instead of the tuning fork resonator, the length-extensional mode quartz crystal resonator may be housed in the unit.

[0078] In addition, a member of the case and the lid is ceramics or glass and a metal or glass, respectively, and a connecting member is a metal or glass with low melting point. Also, a relationship of the resonator, the case and the lid described in this embodiment is applied to a quartz crystal oscillator of the present invention which will be described in FIG. 10.

[0079]FIG. 10 shows a cross-sectional view of a quartz crystal oscillator, which constructs an electronic apparatus of the fifth embodiment of the present invention. The quartz crystal oscillator 190 comprises a quartz crystal oscillating circuit, a case 91 and a lid 92. In this embodiment, circuit elements constructing the oscillating circuit are housed in a quartz crystal unit comprising a flexural mode, quartz crystal tuning fork resonator 90, the case 91 and the lid 92. Also, the oscillating circuit of this embodiment comprises an amplifier 98 including a feedback resistor, the resonator 90, capacitors (not shown here) and a drain resistor (not shown here), and a CMOS inverter is used as the amplifier 98.

[0080] In addition, in this embodiment, the resonator 90 is mounted at a mounting portion 94 of the case 91 by conductive adhesives 96 or solder. As described above, the amplifier 98 is housed in the quartz crystal unit and mounted at the case 91. Also, the case 91 and the lid 92 are connected through a connecting member 93. The resonator 90 of this embodiment is the same as one of the flexural mode, quartz crystal tuning fork resonators 10 and 45 described in detail in FIG. 4-FIG. 7. Also, instead of the tuning fork resonator, the length-extensional mode quartz crystal resonator may be housed in the unit.

[0081] Likewise, in this embodiment, a piece of flexural mode, quartz crystal tuning fork resonator is housed in the unit, but the present invention also includes a quartz crystal unit having a plurality of flexural mode, quartz crystal tuning fork resonators, and at least two of the plurality of resonators are connected electrically in parallel. In addition, the at least two resonators may be an individual resonator or may be individual resonators that are formed integrally at each tuning base through a connecting portion.

[0082] Next, a method for manufacturing a quartz crystal oscillator, which constructs an electronic apparatus of the present invention, is described in detail, according to the manufacturing steps.

[0083]FIG. 11 shows an embodiment of a method for manufacturing a quartz crystal oscillator, which constructs an electronic apparatus of the present invention and a step diagram embodying the present invention. The signs of S-1 to S-12 are the step numbers. First, S-1 shows a cross-sectional view of a quartz crystal wafer 140. Next, in S-2 metal film 141, for example, chromium and gold on the chromium are, respectively, disposed on upper and lower faces of the quartz crystal wafer 140 by an evaporation method or a spattering method. In addition, resist 142 is spread on said metal film 141 in S-3, and after the metal film 141 and the resist 142 were removed except those of tuning fork shape by a photo-lithographic process and an etching process, the tuning fork shape with tuning fork tines 143, 144 and a tuning fork base 145, as be shown in S-4, is integrally formed by a chemical etching process. When the tuning fork shape is formed, cut portions may be formed at the tuning fork base. In FIG.11, the formation of a piece of tuning fork shape is shown, but, a number of tuning fork shapes are actually formed in a piece of quartz crystal wafer.

[0084] Similar to the steps of S-2 and S-3, metal film and resist are spread again on the tuning fork shape of S-4 and grooves 146, 147, 148 and 149 each of which has two step difference portions along the length direction of the tuning fork tines, are formed at the tuning fork tines 143, 144 by the photo-lithographic process and the etching process, and the shape of S-5 is obtained after all of the resist and the metal film were removed. In addition, metal film and resist are spread again on the shape of S-5 and electrodes which are of opposite electrical polarity, are disposed on sides of the tuning fork tines and inside the grooves thereof, as be shown in S-6.

[0085] Namely, electrodes 150, 153 disposed on the sides of the tuning fork tine 143 and electrodes 155, 156 disposed inside the grooves 148, 149 of the tuning fork tine 144 have the same electrical polarity. Similarly, electrodes 151, 152 disposed inside the grooves 146, 147 of the tuning fork tine 143 and electrodes 154, 157 disposed on the sides of the tuning fork tine 144 have the same electrical polarity. Two electrode terminals are, therefore, constructed. In more detail, when an alternating current (AC) voltage is applied between the terminals, the tuning fork tines are capable of vibrating in a flexural mode of inverse phase because said electrodes disposed on step difference portions of the grooves and the electrodes disposed opposite to the said electrodes have opposite electrical polarity. In the step of S-6, a piece of quartz crystal tuning fork resonator capable of vibrating in a flexural mode is shown in the quartz crystal wafer, but a number of quartz crystal tuning fork resonators are actually formed in the quartz crystal wafer.

[0086] In addition, resonance frequency for said resonators is adjusted by a separate step of at least twice and the first adjustment of resonance frequency for said resonators is performed in the quartz crystal wafer by laser or evaporation or plasma etching method so that a frequency deviation of said resonators is within a range of −9000 PPM to +5000 PPM(Parts Per Million). The adjustment of frequency by laser or plasma etching method is performed by trimming mass disposed on tuning fork tines and the adjustment of frequency by an evaporation method is performed by adding mass on tuning fork tines. Namely, those methods can change the resonance frequency of said resonators. Also, the resonators formed in the quartz crystal wafer are inspected therein and when there is a failure resonator, something is marked on it in the quartz crystal wafer or it is removed from the quartz crystal wafer.

[0087] In this embodiment, the tuning fork shape is formed from the step of S-3 and after that, the grooves are formed at the tuning fork tines, namely, the tuning fork tines are formed before the grooves are formed, but this invention is not limited to said embodiment, for example, the grooves are first formed from the step of S-3 and after that, the tuning fork shape may be formed, namely, the grooves are formed before the tuning fork tines are formed. Also, the tuning fork shape and the grooves may be formed simultaneously, namely, the tuning fork tines and the grooves are formed simultaneously.

[0088] There are two methods of A and B in the following step, as be shown by arrow signs. For the step of A, the tuning fork base 145 of the formed flexural mode, quartz crystal tuning fork resonator 160 is first mounted on mounting portion 159 of a case 158 by conductive adhesives 161 or solder, as be shown in S-7. Next, the second adjustment of resonance frequency for the resonator 160 is performed by laser 162 or evaporation or plasma etching method in S-8 so that a frequency deviation is within a range of −100 PPM to +100 PPM. Finally, the case 158 and a lid 163 are connected via glass 164 with the low melting point or a metal in S-9. In this case, the connection of the case and the lid is performed in vacuum because the case 158 has no hole to close it in vacuum.

[0089] In addition, though it is not visible in FIG. 11, the third frequency adjustment may be performed by laser after the step of the connection of S-9 to get a small frequency deviation when a material of the lid is glass. As a result of which it is possible to get the resonator with the frequency deviation which is within a range of −50 PPM to +50 PPM. A frequency capable of vibrating in a fundamental mode is less than 200 kHz, especially, 32.768 kHz is widely used in communication equipment as a time standard. In this step, when the third frequency adjustment is performed, the resonance frequency of said resonators is adjusted so that the frequency deviation by the second frequency adjustment is within a range of −950 PPM to +950 PPM.

[0090] For the step of B, the tuning fork base 145 of the formed resonator 160 is first mounted on mounting portion 159 of a case 165 by conductive adhesives 161 or solder in S-10, in addition, in S-11 the case 165 and a lid 163 are connected by the same way as that of S-9, in more detail, after the resonator was mounted on the mounting portion of the case or after the resonator was mounted at the mounting portion, and the case and the lid were connected, the second adjustment of resonance frequency is performed so that a frequency deviation is generally within a range of −100 PPM to +100 PPM in vacuum, but, it may be within a wider range, for example, −950 PPM to +950 PPM when the third frequency adjustment as will be shown as follows, is performed. Finally, a hole 167 constructed at the case 165 is closed in vacuum using such a metal 166 as solder or glass with the low melting point in S-12.

[0091] Also, similar to the step of A, the third adjustment of resonance frequency may be performed by laser after the step of S-12 to get a small frequency deviation. As a result of which it is possible to get the resonator with the frequency deviation which is within a range of −50 PPM to +50 PPM. Thus, a frequency deviation of the resonators in the case of A and B is finally within a range of −100 PPM to +100 PPM at most. Also, the second frequency adjustment may be performed after the case and the lid were connected and the hole was closed in vacuum. In addition, the hole is constructed at the case, but may be constructed at the lid. Also, the frequency adjustment of the present invention is performed in vacuum or inert gas such as nitrogen gas or atmosphere, and the values described above are values in vacuum.

[0092] Therefore, the flexural mode, quartz crystal tuning fork resonators and the quartz crystal units manufactured by the above-described method are miniaturized and realized with a small series resistance R₁, a high quality factor Q₁ and low price.

[0093] Moreover, in the above-described embodiment, though the first frequency adjustment of the resonators is performed in the quartz crystal wafer and at the same time, when there is a failure resonator, something is marked on it or it is removed from the quartz crystal wafer, but the present invention is not limited to this, namely, the present invention may include the step to inspect the flexural mode, quartz crystal tuning fork resonators formed in the quartz crystal wafer therein, in other words, the step to inspect whether there is a failure resonator or not in the quartz crystal wafer. When there is the failure resonator in the wafer, something is marked on it or it is removed from the wafer or it is remembered by a computer. By including the step, it can increase the yield because it is possible to find out the failure resonator in an early step and the failure resonator does not go to the next step. As a result of which low priced flexural mode, quartz crystal tuning fork resonators can be provided with excellent electrical characteristics.

[0094] In this embodiment, the frequency adjustment is performed three times by a separate step, but may be performed at least twice by a separate step. For example, the third frequency adjustment may be omitted. In addition, in order to construct a quartz crystal oscillator, two electrode terminals of the resonators are connected electrically to an amplifier, capacitors and resistors. In other words, a quartz crystal oscillating circuit is constructed and connected electrically so that an amplification circuit comprises a CMOS inverter and a feedback resistor and a feedback circuit comprises the flexural mode, quartz crystal tuning fork resonator, the drain resistor, the capacitor of a gate side and the capacitor of a drain side. Also, the third frequency adjustment may be performed after the quartz crystal oscillating circuit was constructed.

[0095] Likewise, in the present embodiments the flexural mode quartz crystal resonator of tuning fork type has two tuning fork tines, but embodiments of the present invention include tuning fork tines more than two. In addition, the quartz crystal tuning fork resonators of the present embodiments are housed in a package (unit) of surface mounting type comprising a case and a lid, but may be housed in a package of tubular type.

[0096] In addition, for the tuning fork resonators constructing the quartz crystal oscillators of the first embodiment to the fourth embodiment of the present invention, the resonators are provided so that a capacitance ratio r₁ of a fundamental mode vibration gets smaller than a capacitance ratio r₂ of a second overtone mode vibration, in order to obtain a frequency change of the fundamental mode vibration larger than that of the second overtone mode vibration, versus the same change of a value of load capacitance C_(L). Namely, a variable range of a frequency of the fundamental mode vibration gets wider than that of the second overtone mode vibration.

[0097] In more detail, for example, when C_(L)=18 pF and the C_(L) changes in 1 pF, the frequency change of the fundamental mode vibration becomes larger than that of the second overtone mode vibration because the capacitance ratio r₁ is smaller than the capacitance ratio r₂. Therefore, there is a remarkable effect for the fundamental mode vibration, such that the resonators can be provided with the frequency variable in the wide range, even when the value of load capacitance C_(L) changes slightly. Accordingly, when a variation of the same frequency is required, the number of capacitors which are used in the quartz crystal oscillators decreases because the frequency change versus load capacitance 1 pF becomes large, as compared with that of the second overtone mode vibration. As a result, the low priced oscillators can be provided.

[0098] Moreover, capacitance ratios r₁ and r₂ of a flexural mode, quartz crystal tuning fork resonator are given by r₁=C₀/C₁ and r₂=C₀/C₂, respectively, where C₀ is shunt capacitance in an electrical equivalent circuit of the resonator, and C₁ and C₂ are, respectively, motional capacitance of a fundamental mode vibration and a second overtone mode vibration in the electrical equivalent circuit of the resonator. In addition, the flexural mode, quartz crystal tuning fork resonator has a quality factor Q₁ for the fundamental mode vibration and a quality factor Q₂ for the second overtone mode vibration.

[0099] In detail, the tuning fork resonator of this embodiment is provided so that the influence on resonance frequency of the fundamental mode vibration by the shunt capacitance becomes smaller than that of the second overtone mode vibration by the shunt capacitance, namely, so that it satisfies a relationship of r₁/2Q₁ ² <r₂/2Q₂ ². As a result, the tuning fork resonator, capable of vibrating in the fundamental mode and having a high frequency stability can be provided because the influence on the resonance frequency of the fundamental mode vibration by the shunt capacitance becomes so extremely small as it can be ignored. Also, the present invention replaces r₁/2Q₁ ² with S₁ and r₂/2Q₂ ² with S₂, respectively, and here, S₁ and S₂ are called “stable factor of frequency” of the fundamental mode vibration and the second overtone mode vibration. Namely, S₁ and S₂ are given by S₁=r₁/2Q₁ ² and S₂=r₂/2Q₂ ², respectively.

[0100] In addition, when a power source is applied to the quartz crystal oscillating circuit, at least one oscillation which satisfies an amplitude condition and a phase condition of vibration starts in the circuit, and a spent time to get to about ninety percent of the steady amplitude of the vibration is called “rise time”. Namely, the shorter the rise time becomes, the easier the oscillation becomes. When rise time t_(r1) of the fundamental mode vibration and rise time t_(r2) of the second overtone mode vibration in the circuit are taken, t_(r1) and t_(r2) are given by t_(r1)=kQ₁/(ω₁(−1+|−RL₁|/R₁)) and t_(r2)=kQ₂/(ω₂(−1+|−RL₂|/R₂)), respectively, where k is constant and ω₁ and ω₂ are an angular frequency for the fundamental mode vibration and the second overtone mode vibration, respectively.

[0101] From the above-described relation, it is possible to obtain the rise time t_(r1) of the fundamental mode vibration less than the rise time t_(r2) of the second overtone mode vibration. As an example, when resonance frequency of a flexural mode, quartz crystal tuning fork resonator is about 32.768 kHz for a fundamental mode vibration and the resonator has a value of W₂/W=0.5, t₁/t=0.34 and l₁/l=0.48, though there is a distribution in production, as an example, the resonator has a value of Q₁=62,000 and Q₂=192,000, respectively. In this embodiment, Q₂ has a value of about three times of Q₁. Accordingly, to obtain the t_(r1) less than the t_(r2), it is necessary to satisfy a relationship of |−RL₁|/R₁>2|−RL₂|/R₂−1 by using a relation of ω₂=6 ω₁ approximately. Also, according to this invention, the relationship is not limited to the quartz crystal oscillating circuit comprising the resonator in this embodiment, but this invention includes all quartz crystal oscillating circuits to satisfy the relationship. By constructing the oscillating circuit like this, a quartz crystal oscillator with the flexural mode, quartz crystal tuning fork resonator can be provided with a short rise time. In other words, an output signal of the oscillator has a frequency of a fundamental mode vibration of the resonator and is outputted through a buffer circuit. Namely, the second overtone mode vibration can be suppressed in the oscillating circuit. In this embodiment, the resonator has also a value of r₁=320 and r₂ =10,600 as an example.

[0102] The above-described quartz crystal resonators are formed by at least one method of chemical, mechanical and physical methods. The mechanical method, for example, uses a particle such as GC#1000 and the physical method, for example, uses atom or molecule. Therefore, these methods are called “a particle method” here.

[0103] Thus, the electronic apparatus of this invention comprising a display portion and a quartz crystal oscillator at least may operate normally because the quartz crystal oscillator comprises the quartz crystal oscillating circuit with a high frequency stability, namely, a high frequency reliability.

[0104] As described above, it will be easily understood that the electronic apparatus comprising the quartz crystal oscillator comprising the quartz crystal oscillating circuit having the flexural mode, quartz crystal tuning fork resonator with novel shapes, the novel electrode construction and excellent electrical characteristics, according to the present invention, may have the outstanding effects. Similar to this, it will be easily understood that the electronic apparatus comprising the quartz crystal oscillator comprising the quartz crystal oscillating circuit having the length-extensional mode quartz crystal resonator with the novel cutting angle and the novel shape, according to the present invention, may have also the outstanding effect. In addition to this, while the present invention has been shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the changes in shape and electrode construction can be made therein without departing from the spirit and scope of the present invention. 

What is claimed is:
 1. An electronic apparatus comprising a display portion and a quartz crystal oscillator at least, said electronic apparatus having one quartz crystal oscillator, said one quartz crystal oscillator comprising: a quartz crystal oscillating circuit comprising; an amplification circuit comprising an amplifier at least and a feedback circuit comprising a quartz crystal resonator and capacitors at least, said quartz crystal resonator being a quartz crystal tuning fork resonator capable of vibrating in a flexural mode, said quartz crystal tuning fork resonator comprising: tuning fork tines each of which has a length, a width and a thickness and the length greater than the width and the thickness; and a tuning fork base; said tuning fork tines and said tuning fork base that are formed integrally; electrodes disposed facing each other on sides of said tuning fork tines so that the electrodes disposed facing each other are of opposite electrical polarity and said tuning fork tines are capable of vibrating in inverse phase, and a ratio of an absolute value of negative resistance, |−RL₁| of a fundamental mode vibration of said amplification circuit and series resistance R₁ of the fundamental mode vibration being larger than that of an absolute value of negative resistance, |−RL₂| of a second overtone mode vibration of said amplification circuit and series resistance R₂ of the second overtone mode vibration, wherein said quartz crystal oscillating circuit comprises said quartz crystal tuning fork resonator whose figure of merit M₁ of the fundamental mode vibration is larger than figure of merit M₂ of the second overtone mode vibration to suppress the second overtone mode vibration and to get a high frequency stability for the fundamental mode vibration, and a ratio of an amplification rate α₁ for the fundamental mode vibration and an amplification rate α₂ for the second overtone mode vibration of said amplification circuit is larger than that of a feedback rate β₂ of the second overtone mode vibration and a feedback rate β₁ of the fundamental mode vibration of said feedback circuit and a product of the amplification rate α₁ and the feedback rate β₁ of the fundamental mode vibration is larger than 1, and wherein an output signal of said quartz crystal oscillating circuit comprising said quartz crystal tuning fork resonator capable of vibrating in the flexural mode has a frequency of the fundamental mode vibration of said resonator and is outputted through a buffer circuit, and said output signal is a clock signal which is used to display time at said display portion of said electronic apparatus.
 2. The electronic apparatus according to claim 1, wherein said frequency of the fundamental mode vibration is within a range of 10 kHz to 200 kHz.
 3. The electronic apparatus according to claim 2, wherein said amplification circuit comprises a CMOS inverter and a feedback resistor, and said feedback circuit comprises said quartz crystal tuning fork resonator, a drain resistor, a capacitor of a gate side and a capacitor of a drain side.
 4. The electronic apparatus according to claim 3, wherein capacitance ratio r₁ of the fundamental mode vibration of said resonator is smaller than capacitance ratio r₂ of the second overtone mode vibration.
 5. The electronic apparatus according to claim 4, wherein S₁ is less than S₂ when stable factors of frequency S₁ and S₂ of the fundamental mode vibration and the second overtone mode vibration of said resonator are given by S₁=r₁/2Q¹ ² and S₂=r₂/2Q₂ ², respectively.
 6. The electronic apparatus according to claim 5, wherein a tuning fork base of said resonator has cut portions.
 7. The electronic apparatus according to claim 5, wherein said quartz crystal oscillating circuit has load capacitance C_(L) less than 18 pF.
 8. The electronic apparatus according to claim 5, wherein series resistance R₁ of the fundamental mode vibration of said resonator is less than series resistance R₂ of the second overtone mode vibration.
 9. The electronic apparatus according to claim 8, wherein a ratio of groove width W₂ and tine width W is larger than 0.35 and less than 1, and a ratio of groove thickness t₁ and tine thickness t is less than 0.79.
 10. An electronic apparatus comprising a display portion and a quartz crystal oscillator at least, said electronic apparatus comprising at least one quartz crystal oscillator, said at least one quartz crystal oscillator comprising: a quartz crystal oscillating circuit comprising; an amplification circuit comprising an amplifier at least and a feedback circuit comprising a quartz crystal resonator and capacitors at least, said quartz crystal resonator being a length-extensional mode quartz crystal resonator capable of vibrating in a length-extensional mode, and said length-extensional mode quartz crystal resonator comprising: a vibrational portion having a length greater than a width and a thickness smaller than the width; connecting portions located at ends of said vibrational portion; supporting portions connected to said vibrational portion through said connecting portions; and electrodes disposed on upper and lower faces of said vibrational portion, wherein a piezoelectric constant e₁₂ of said resonator is within a range of 0.095 C/m² to 0.18 C/m² in the absolute value, and wherein an output signal of said quartz crystal oscillating circuit comprising said length-extensional mode quartz crystal resonator is outputted through a buffer circuit, and said output signal is a clock signal which is used except time display of said electronic apparatus.
 11. The electronic apparatus according to claim 10, wherein a cutting angle of said resonator is within a range of XYtl(−30°-+30°)/(−40°-+40°).
 12. A method for manufacturing an electronic apparatus comprising a display portion and a quartz crystal oscillator at least, said electronic apparatus comprising at least one quartz crystal oscillator, said at least one quartz crystal oscillator comprising: a quartz crystal oscillating circuit comprising; an amplification circuit comprising an amplifier at least and a feedback circuit comprising a quartz crystal resonator and capacitors at least, said quartz crystal resonator being a quartz crystal tuning fork resonator capable of vibrating in a flexural mode, said quartz crystal tuning fork resonator comprising the steps of: forming integrally tuning fork tines each of which has a length, a width and a thickness and the length greater than the width and the thickness and a tuning fork base; disposing electrodes facing each other on sides of said tuning fork tines so that the electrodes that is disposed facing each other are of opposite electrical polarity and said tuning fork tines are capable of vibrating in inverse phase; and adjusting resonance frequency of said quartz crystal tuning fork resonator after mounting it at a mounting portion by conductive adhesives or solder so that a frequency deviation is within a range of −100 PPM to +100 PPM, and said at least one quartz crystal oscillator comprising the step of: constructing said quartz crystal oscillating circuit so that a ratio of an absolute value of negative resistance, |−RL₁| of a fundamental mode vibration of said amplification circuit and series resistance R₁ of the fundamental mode vibration is larger than that of an absolute value of negative resistance, |−RL₂| of a second overtone mode vibration of said amplification circuit and series resistance R₂ of the second overtone mode vibration, wherein said quartz crystal oscillating circuit comprises said quartz crystal tuning fork resonator whose figure of merit M₁ of the fundamental mode vibration is larger than figure of merit M₂ of the second overtone mode vibration to suppress the second overtone mode vibration and to get a high frequency stability for the fundamental mode vibration, and a ratio of an amplification rate α₁ for the fundamental mode vibration and an amplification rate α₂ for the second overtone mode vibration of said amplification circuit is larger than that of a feedback rate β₂ of the second overtone mode vibration and a feedback rate β₁ of the fundamental mode vibration of said feedback circuit and a product of the amplification rate α₁ and the feedback rate β₁ of the fundamental mode vibration is larger than 1, and wherein an output signal of said quartz crystal oscillating circuit comprising said quartz crystal tuning fork resonator capable of vibrating in the flexural mode has a frequency of the fundamental mode vibration of said resonator and is outputted through a buffer circuit, and said output signal is a clock signal which is used to display time at said display portion of said electronic apparatus.
 13. The method of claim 12, wherein said amplification circuit comprises a CMOS inverter and a feedback resistor, and said feedback circuit comprises said quartz crystal tuning fork resonator, a drain resistor, a capacitor of a gate side and a capacitor of a drain side.
 14. The method of claim 12, wherein the value of |−RL₁|/R₁ is greater than the value of 2|−RL₂|/R₂−1.
 15. The method of claim 12, comprising the further step of forming flexural mode, quartz crystal tuning fork resonators in a quartz crystal wafer simultaneously by at least one method of chemical, mechanical and physical methods.
 16. The method of claim 15, comprising the further steps of inspecting if there is a failure resonator or not in the quartz crystal wafer and removing the failure resonator from the quartz crystal wafer. 